This invention is directed to electronic apparatus for measuring the contamination resistance associated with electrical contacts contained on a printed circuit board. It more specifically addresses circuitry utilized in conjunction with a probe which engages the contacts in order to measure the contamination resistance.
It is important that the contacts of a connector assembly associated with a printed circuit board do not exhibit excessive resistance to pins which will engage the contacts in order to minimize the attenuation of signals which will pass through the contact/pin coupling. Contamination resistance is the resistance associated with a film or layer of material on the contact which separates an inserted pin from the base metal or the plated surface of the contact. The total resistance associated with a pin inserted in a contact includes the resistances of the pin and contact materials, the contact resistance between the pin and the contact, and the contamination resistance. Contact resistance is the resistance that would normally be present at the physical area of contact between a clean pin and a clean contact.
It is desirable to be able to measure the contamination resistance associated with printed circuit board contacts in order to insure that excessive resistance will not be presented when the board is installed. Excessive resistance will result in attenuated signals or discontinuities in which the signal will not be coupled at all. Difficulties have been encountered in attempting to make resistance contamination measurements which are repeatable due to the low resistance values normally associated with such measurements.